1. Field of the Invention
The present invention relates to a kind of printed antenna, more particularly a printed antenna suitable for MIMO wireless networking device and a wireless networking device having the same.
2. Description of the Prior Art
FIG. 1 depicts the perspective view of a typical wireless networking device 10, comprising a body 11, internal circuitry 12 disposed inside the body, a connecting member 13 disposed at one end of body 11 to connect an external host (not shown in the figure), and an antenna signal transceiver 14 arranged on the other end of body 11 and corresponding to the connecting member 13. Generally, the shell of antenna signal transceiver 14 is made of non-metallic material. When the wireless networking device 10 is connected to an external host, the antenna signal transceiver 14 must be exposed outside the external host for effective receiving and transmission of wireless signals. Based on the practice of regular users, the X-Y plane as shown in FIG. 1 should be the plane with better wireless signal transmission. Thus the design of antenna for wireless networking device 10 focuses primarily on how to improve the isolation between antennas mounted in X-Y direction and reduce the dead space in the radiation pattern of antenna so as to enhance the receiving and transmitting ability of antenna on X-Y plane.
FIG. 2 depicts the diagram of a conventional internal circuitry 20 in a MIMO wireless networking device. The conventional internal circuitry 20 comprises a base plate 21, a control circuit disposed on the base plate 21, a grounding member 23 covering a predefined area of base plate 21, and an antenna unit 24 electrically connected to the control circuit 22.
Antenna design that complies with the MIMO spec wireless networking device uses three antennas to form a three transmitter/two receiver antenna unit. For example, in the conventional MIMO antenna unit 24 as shown in FIG. 2, it includes a first antenna 241 configured in the middle, and a second antenna 242 and a third antenna 243 disposed respectively on each side of first antenna 241. The three antennas 241, 242, 243 are monopole antennas adjacent to each other and facing the same direction (i.e. in X direction on the right side of FIG. 2). The three antennas 241, 242, 243 respectively pass (cross) through grounding member 23 to connect to control circuit 22 via a first, a second and a third feedline 251, 252, 253 and are driven and controlled by the control circuit 22. A major drawback in this kind of conventional MIMO antenna unit 24 is that its three monopole antennas 241, 242, 243 are arranged next to each other and extend in the same direction, resulting in inadequate isolation between adjacent antennas (e.g. between first antenna 241 and second antenna 242). In addition, the design of using monopole for first antenna 241 results in bigger dead space in the radiation pattern on the X-Y plane. FIG. 3 shows the radiation pattern measured from the X-Y plane of first antenna 241 used by the conventional MIMO antenna unit 24 as depicted in FIG. 2. As shown, the maximum horizontal gain of conventional first antenna 241 is merely −0.79 dBi, meaning there is practically no gain. FIG. 4 illustrates the isolation graph measured between first antenna 241 and second antenna 242 in the conventional MIMO antenna unit 24 as shown in FIG. 2. Based on the graph, the isolation between conventional first antenna 241 and second antenna 242 in the operating frequency range of 2.4 GHz and 2.5 GHz is approximately −6.01 dB, which is still higher than the −10 dB or under requirement in the market for high-performance antenna and leaves room for further improvement.